The present invention relates generally to power supply systems, and specifically to monitoring current in a power supply system consisting of parallel power supplies.
Large electronic systems frequently use power supply systems consisting of multiple supplies operating in parallel. Multiple power supplies in a distributed power system are often required in order to supply the high level of current drawn by these large systems. The demand for higher load current is caused by improved performance and increased functionality of electronic systems. The difficulty of supplying sufficient current is aggravated by the relatively low supply voltages demanded by many circuits, particularly digital circuits. Thus, high current loads are often supplied by several power supplies connected in parallel.
The use of multiple parallel power supplies can improve system reliability, compared with the use of a single high current output power supply, particularly when the number of parallel power supplies used exceeds the minimum number needed by at least one, because failure of a single power supply need not cause the entire system to shut down.
It is frequently useful to monitor the current drawn by an electronic system, in order to track power output. Monitoring the current level may be used to protect the power system, for example by tripping a circuit breaker if the current drawn is excessive. Typically, current is monitored, and electronic circuit breakers implemented, using a sense resistor to sense the current through a conductor, or alternatively using a Hall Effect device. If the current becomes excessive, a breaker may be tripped. A disadvantage to these approaches to monitoring current and protecting the power system is that each requires the addition of circuitry to the power supply system. Additionally, the voltage drop across the sense resistor results in both a power loss and an error in the output voltage.
It is therefore desirable to provide a method for monitoring current in a parallel power supply system, and potentially triggering a circuit breaker, that does not require additional circuitry, and does not result in an output voltage error.
In summary, the present invention is a system and method for monitoring current and protecting a power supply system from excessive current loading using the error voltage generated by current share controller devices in the power supply system. This error voltage is used by a central processing unit (CPU), along with a signal indicating the total number of power supplies, to calculate the total current supplied by the power supply system.
Current share controller devices are used in power supply systems to balance the load current among parallel connected power supplies. Each power supply in the distributed system is provided with a current load controller device. The power supply with the highest voltage is designated as the master. Its current load controller measures a small voltage across a current sense resistor and develops an error voltage that drives a xe2x80x9cshare bus.xe2x80x9d The error voltage on the share bus is monitored by all the other power supplies and used by them to control how much current they supply. Since all the power supplies are trying to match an internal error voltage with the error voltage on the share bus, they all supply substantially identical amounts of current, and therefore the load is balanced equally among the supplies.
The error voltage generated by the master power supply is proportional to the current drawn from the master power supply. Once the load is balanced, each power supply will have the substantially the same current drawn from it as the master supply. Therefore, the total current may be determined from the error voltage, when the number of power supplies in the system is known, without adding any additional circuitry for current monitoring.
The total number of power supplies may be determined by supplying a small current source along with each power supply, and connecting the current sources to a common bus. The current provided by each power supply is called the xe2x80x9cdevice presentxe2x80x9d current. The total current on the xe2x80x9cdevice presentxe2x80x9d busxe2x80x94the xe2x80x9cpresent currentxe2x80x9d xe2x80x94thus indicates how many power supplies are present. The error voltage from the share bus, and the current from the present bus, may be provided to a control circuit, that includes a CPU. The error voltage and present current signal may be converted to digital signals using an analog-to-digital converter, and provided to the CPU. Using the present signal, the CPU calculates the total number of power supplies present. Using the error voltage signal and the current gain for the share load controller, the CPU calculates the current per power supply. The CPU then calculates the total current using the current per power supply and the number of power supplies present. The CPU thus is capable of monitoring the total current in the system. If the total current exceeds some predetermined threshold, a circuit breaker can be triggered by the CPU, shutting down the power supplies.